Why do you think the zygote is dormant for sometime in a fertilised ovule?
The zygote remains dormant in a fertilised ovule because endosperm development precedes embryo development. The Primary Endosperm Cell (PEC) divides repeatedly to form the triploid endosperm tissue first. This endosperm contains abundant reserve food materials that are essential for the nutrition of the developing embryo.
Additionally, as the seed matures, its water content is reduced to about 10-15 per cent moisture by mass, making seeds relatively dry. This causes the general metabolic activity of the embryo to slow down, leading to a state of inactivity called dormancy. The zygote remains in this dormant state until favourable conditions (adequate moisture, oxygen, and suitable temperature) are available for germination.
Explanation
According to the textbook context, there are two main reasons for zygote dormancy: (1) Endosperm development must occur first to provide nutrition to the developing embryo, as stated 'Endosperm development precedes embryo development' and the endosperm cells 'are filled with reserve food materials and are used for the nutrition of the developing embryo'; (2) During seed maturation, water content reduces to 10-15% causing reduced metabolic activity and dormancy until favourable conditions for germination are available.
Solution Steps
Step 1: Identify that endosperm development must occur first to provide nutrition to the embryo
Step 2: Explain that reduced water content during seed maturation slows metabolic activity
Step 3: Connect dormancy to waiting for favourable conditions for germination